Power bank



FIG. 1 is a perspective view of a power bank, showing my new design;

FIG. 2 is a top view thereof;

FIG. 3 is a bottom view thereof;

FIG. 4 is a right view thereof;

FIG. 5 is a left view thereof;

FIG. 6 is a back view thereof; and,

FIG. 7 is a front view thereof.

The broken lines in the drawings are for the purpose of illustrating unclaimed portions of the power bank and form no part of the claimed design. 

CLAIM The ornamental design for a power bank, as shown and described. 